Past Paper Questions Flashcards
Describe the role of membranes [in an Amoeba]:
Control what, enters / leaves, the organelles
(Contains receptors to) detect changes in environment.
Compartmentalisation
Site for enzymes / electron carriers / components of metabolic pathways
To create concentration gradients
What is meant by translocation?
The transport of sucrose from source to sink.
How does water move in the apoplast pathway?
Water passes between cells and through the cell walls.
How does water move in the symplastic pathway?
Water enters the cell cytoplasm by osmosis and passes from cell to cell via junctions called plasmodesmata.
At the endodermis layer, water passing between the cells must enter the symplast pathway because passage between the cells is blocked by the Casparian strip.
Explain how increased air movement increases the loss of water vapour from the leaves:
Water vapour around the leaf is blown away.
(Water potential around the stomata is reduced).
The water potential gradient (between the leaf and air) increases, encouraging evaporation.
From the start of mitosis, describe the events that have taken place to enable the cell to have reached anaphase:
Chromosomes have condensed
The nuclear envelope disintegrates and the nucleolus is no longer visible
Centrioles move to opposite ends/piles of the cell
Spindle fibres attach to the centromeres of chromosomes and they align in the equator of the cell
The spindle fibres then shorten, pulling the chromosomes towards the poles of the cell.
Use your knowledge of the mechanisms of water transport to explain the movement of water through a plant:
- Water is lost by evaporation / transpiration
- (Water moves by) symplast and apoplast pathways
- Water then moves through / along cell walls by capillary action / adhesion via the apoplast pathway
- Meanwhile, water loss reduces the water potential of (leaf) cells
- Water moves from higher water potential to lower water potential / down water potential gradient by osmosis (symplast pathway) through plasmodesmata (symplast pathway)
Define the term ‘parasite’:
An organism which lives in / on the host (NOT off the host).
It gains nutrition / feeds from (host) at the expense of / harms (host).
Describe how the structure of antibodies allows them to perform their function:
2 light chains and 2 heavy chains / 4 polypeptide chains
Variable region allows binding to antigens
Two variable regions allow binding of more than one (of the same) antigen
Variable region on different antibodies allows specificity to different antigens
Constant region allows recognition by binding to phagocytes
Hinge (region) allows flexibility
Disulfide bonds / bridges hold the polypeptides / light and heavy chains together
Outline the mode of action of antibodies in defending the body against pathogens by describing the processes of i) neutralisation and ii) agglutination:
Neutralisation:
The antibodies cover the binding site / antigen on pathogen
They bind to toxins and prevent their entry into a host cell
Agglutination:
They clump together with many pathogens.
The clumps are too large to enter the host cell / cross
membranes. This also increases the likelihood of being consumed by phagocytes.
Describe how to do the emulsion test for lipids and how a positive result would be identified:
Mix the substance being tested with ethanol and water.
If lipids are present, the solution goes cloudy.
Where is mRNA produced?
The nucleus (NOT nucleolus)
State 2 reasons why mammals need a mass transport system:
Any 2 from:
Mammals have a small surface area to volume ratio / mass transport system provides a large surface area to volume ratio
High activity levels
High metabolic rate
They’re multicellular
Name the type of molecule formed when 2 amino acids are joined together:
Dipeptide
Describe how the molecular structure of haemoglobin enables it to transport oxygen molecules.
(Details of oxygen dissociation curves are not required).
(Haemoglobin) has four polypeptide chains
(Hhaemoglobin) has four prosthetic / haem groups
Haem / prosthetic group contains iron (ion)
Each , iron (ion) / haem ,
can carry one oxygen molecule
Forms oxyhaemoglobin ;
Explain the importance of complementary base pairing in DNA:
It makes sure DNA is replicated accurately / correctly
It reduces chances of mutation
In what order would CVS and amniocentesis be carried out?
Chronic villus sampling can be carried out earlier in the pregnancy then amniocentesis.
It has a higher risk of miscarriage then amniocentesis and carries a slight risk of producing fetal deformities.(conducted at 10 to 15 weeks)
Amniocentesis is used between week 15 and 20.
Although it carries a small risk of miscarriage, the probability of this occurring is less than for CVS.
What is Ras?
And example of unregulated cell division.
In a healthy cell, division is only triggered by the Ras gene product when the cell is stimulated.
When the Ras gene is mutated it becomes an oncogene, it stimulates cell division continually and cell cycle inhibition is removed.
What’s c-Myc?
In the human genome, it is a regulator gene responsible for regulating the expression of many genes.
When mutated it is found in many cancers and causes the Myc gene to be constantly expressed (a transcription factor is constantly being produced). This leads to unregulated expression of many genes. (Oncogene)
What’s the p53 gene?
It’s vital as, when DNA is damaged, it activates proteins which repair the DNA.
It can temporarily stop the cell cycle to allow the proteins to repair the DNA.
It can also initiate apoptosis.
(Tumour suppressor gene)
Describe how HIV is transmitted and how the spread can be controlled:
It spreads from person to person in body fluids
• named example e.g. from mother to baby in uterus
Once in blood virus enters T lymphocytes. It may remain dormant for long period
Controlling the spread:
• screening donated blood
• education
• named example e.g. giving sterile needles to drug users
• epidemiological testing
• access to means of prevention e.g. condom clinics
Why are HIV positive people at a greater risk of developing TB than those without HIV?
They have a weak(ened) /compromised, immune system.
T helper cells are destroyed / their numbers fall
(T helper cells normally) activate, other immune cells / B cells
Fewer / no antibodies produced
Suggest how smoking during pregnancy can have a negative effect on the baby?
Carbon monoxide combines with haemoglobin ;
Nicotine reduces diameter of blood vessels (in placenta and fetus)
This reduces oxygen supply to the fetus - fetus’s heart beats faster
(Increased chance of) premature birth
(Increased chance of) low birth weight
Baby’s lungs less well developed
Higher risk of still birth / death in early infancy
Describe how a karyotype is obtained from amniotic fluid or chronic villi:
1) Culture cells.
2) (Chemical added to) stimulate cells to divide / undergo mitosis.
3) Stop spindle fibres being formed / division at beginning of metaphase.
4) This is done by adding colchicine.
5) (Before staining) - (dilute) salt solution added
(to burst cells).
6) (Before sorting) the chromosomes / DNA are stained.
7) (Finally) The chromosomes are sorted into pairs.
Describe how non-disjunction can lead to genetic disorders:
[Specific example in paper]
The pair of (homologous) chromosomes fail to separate during anaphase 1 / anaphase 2
One gamete / cell receives 2 X chromosomes
when fertilisation happens.
This results in a zygote / fertilised egg fetus with 47 chromosomes.
Name the bind broken by lipases:
Ester
Outline the function of the myelin sheath in the transmission of nerve impulses in somatic motor neurones: (2)
It speeds up conduction of nerve impulse
It allows saltatory conduction / the impulse can jump from node to node
State one similarity and one difference between somatic and autonomic motor neurones, other than the distribution of myelin sheath:
(Somatic motor neurone completely myelinated whereas, in autonomic, only preganglionic neurone is myelinated)
Similarity:
- Both have a cell body
- Both have a synapse to effectors
Difference:
- Somatic motor neurone is continuous/only one neurone whereas autonomic has two parts/neurones.
- Autonomic has ganglion
- Somatic effectors are skeletal muscles. Autonomic effectors are smooth muscle
Outline how the autonomic nervous system acts on cardiac muscle to regulate the supply of oxygen and glucose to the tissues:
(6)
Sympathetic:
- Sympathetic (branch) speeds up heart rate
- It (acts on) sino-atrial node / SAN / pacemaker
- It increases the rate of ventricle contraction
- It increases cardiac output / stroke volume
- More oxygen to meet increased demands of muscles
Parasympathetic:
- Parasympathetic (branch) slows heart rate
- This reduces cardiac output
- Less oxygen to meet lower demands of muscles
Blood transports, oxygen / glucose
… for aerobic respiration
Discuss why hormone treatments could be considered both ethical and unethical:
(For girls with turners syndrome:
Human Growth Hormone given at 2-5 yrs.
Oestrogen replacement therapy begins at 12-15 yrs)
Ethical:
- Enables child to lead normal life
- Child isn’t discriminated against
- Oestrogen allows secondary sex characteristics to develop
- Oestrogen reduces risk of osteoporosis
- HGH enables child to reach normal height
Unethical:
- Child isn’t given a choice (for HGH)
- Treatment could be uncomfortable
- People should be accepted as they are
- Long term treatment with Oestrogen could increase risk of cancer
Discuss ethical reasons why genetic engineering of human cells [to produce offspring] is not an option which a genetic counsellor would recommend:
It’s reproductive cloning
Its illegal (in UK)
It could lead to eugenics / designer babies
Technique not tried on humans
Could lead to mutations
Parents are only carriers / could have a normal child
Could use IVF using donor
Describe how genetic engineering has the potential to provide non-human organs for transplantation:
Discuss why some may object to the use of such organs:
Genetic engineering non human organs:
- foreign/ non-self tissue will be rejected by the body
- genetic modification to prevent rejection, due to antigens on cell surface membranes
- modifying / silencing genes for antigen (expression) so fewer antigens present
Objections:
- May involve unethical treatment of animals
- May lead to virus transfer to humans
- May hold specific objections on religious grounds
- Animals turn into a commodity
Suggest what is meant by the term ‘therapeutic’:
It has a healing /beneficial effect
Suggest 2 conditions for which cannabis can be used therapeutically:
Multiple sclerosis / MS Cancer Parkinson’s disease Arthritis Cystic fibrosis Migraine Glaucoma Alzheimer’s
Outline how breakdown products from drugs pass from blood plasma into urine:
By ultrafiltration
They pass from the glomerulus / capillaries into Bowman’s / renal capsule and are forced out by high hydrostatic pressure.
Not all is reabsorbed / some remains in the kidney tubule and passes into the ureter / bladder.
State 2 symptoms of cannabis intoxication:
Talkative/cheerful
Not aware of surroundings
Hallucinations
Anxiety and depression
Relaxed
Dilated pupils
Explain why the frequency of the sickle cell allele is higher in areas like west Africa [where malaria is an endemic) :
Malaria acts as a selection pressure.
Heterozygotes / carriers of sickle cell are less likely to get malaria.
This advantageous allele is passed on.
Homozygous ‘normal’ individuals die from malaria (HbA HbA).
Homozygous for sickle cell die from anaemia (HbA HbS).
Explain how an automated sequencing machine orders the DNA fragments from the PCR reaction into size order:
By electrophoresis.
The (negative) DNA moves towards the anode / positive electrode.
Smaller fragments move faster, thus moving farther.
Explain the difference between somatic cell gene therapy and germ line cell gene therapy:
Somatic cell gene therapy:
- cannot be inherited
- introduces a functional gene into the patient / non reproductive cell
- only some cells have the functional gene/allele
- temporary / needs to be repeated
Germ line cell gene therapy:
- can be inherited
- all cells have the functional gene
- permanent
Describe how dopamine can produce an excitatory post-synaptic potential:
It binds to receptors on the postsynaptic membrane.
Sodium channels open.
Sodium diffuses into the post synaptic neurone.
What type of motor neurone stimulates contraction of skeletal muscle?
Somatic (voluntary)
State the importance of the intermembrane space for mitochondrial function?
To establish a proton gradient, across inner membrane
Explain why a knockout of the gene encoding GnRH causes infertility in female mice:
FSH and LH not released.
The follicle isn’t stimulated.
What are disulfide bonds?
Covalent binds between cysteine amino acids.
Outline how blood pressure can be measured manually:
The cuff of a sphygmomanometer cuts off the blood flow to the brachial artery (of the arm).
A stethoscope is then used to listen to blood flow.
The cuff is slowly relaxed / the valve is released.
The first sound indicates systolic pressure. Disappearance of sound indicates diastolic pressure.
Explain how fMRI measures brain activity:
It shows which parts of the brain are active.
Magnetic properties of oxyhaemoglobin and
deoxyhaemoglobin different.
Higher blood flow / oxygen uptake in active regions results in greater emission of radio signal from active regions.
This produces a 3D image.
